Photo-electric cell system



p 1934- A. EULENHOFER PHOTO ELECTRIP CELL SYSTEM Filed Dec. 14, 1929 Inventor fldol-f fqlenllb'f l Patented Sept. 4, 1934 omrsb .sTA

TE-S- PAT PHOTO-ELECTRIC CELL SYSTEM Adolf Eulenhiifer, Berlin-rem pelhof, Germany,

Germany assignor to C. Lorenz, A. G., Berlin,

Application December 14, 1929, Serial Noumea- In Germany February 11, 1929 9 Claimm'lCl. 173 5) This invention refers to photo-electric cell systemsand more particularly to photo-electric cell arrangements as used for photo-telegraphic or picture transmission.

5 The object of this invention consists in providing means in connection with a photo-electric cell, whereby the photo-electric output current varies periodically according to a definite frequency with its amplitudes, changing in accord- 10 ance with the light values of the successive elementary picture portions scanned by the transmitting apparatus.

Another object of the invention is to provide a simple and effective means, free from mechanical it moving elements, for producing a periodic output current of the cell with an amplitude varying in accordance with the input signaling currents to be used for signalingpurposes.

This and any further objects in details of construction, as well as operation, will become apparent by the detailed description which follows; This description is taken in. reference to the accompanying drawing, or which Figure 1 shows, in a schematic manner, a dialated in accordance with the light values of the elementary picture portions, may then be amplified by means of thewell-known more eifective amplifying systems, using inductive and capacitative coupling elements. 60 According to the present invention, another method is proposed for directly producing a modulated carrier current in a photo-electric cell. In accordance with the invention, an additional source of light is provided besides the scanning light source of the picture transmission apparatus, the former varying in the rhythm of the desired carrier frequency. This scheme hasnothing to do with the well-known arrangement of applying a biasing illumination upon the 70 photo-electric electrode of the cell which serves the purpose of securing the most efiicient operation at the most favorable operating point-on the photo-electric cell characteristic. In order to carry the invention into efl'ect, it is necessary, 75

however, to use a light source which is capable I of readily following the oscillations of the modugram of a picture scanningsystem, having the invention embodied therein.

Figures 2 and 3 are explanatory theoretical curves illustrating the physical operation of the novel photo-electric translating device, as illustrated by Figures 1 and 2.

The amplification of electric current variations as supplied by photo-electric cells, meets with difliculties, as these photo-electric currents are uni-directional currents, and accordingly, they have to be amplified by means of direct current amplifiers. It is well'known in the art that in order to amplify weak direct current impulses, no capacities or inductivities can be used as coupling elements for the amplifying tubes. For amplifi- -4i) cation of this kind, only direct or galvanic coupling can be employed. In order to overcome these difiiculties, a number of schemes have been proposed for avoiding a direct current amplification One of these methods consists in, that the beam of light reflected from the picture under scanning is chopped by means of a perforated rotating disc whereby the photo-electric cell supplies a pulsating direct current; However, the use of such a perforated disc or chopper prelating frequency. For such a light source, for instance, a glow lamp may be used which may be ignited and extinguished at a very rapid rate.

Referring more particularly to the drawing, which shows, by example, one form of embodimerit of the invention, a picture drum or cylinder C is shown upon which, according to the 'known practice, the picture or document which 'of the incident beam of light, and the amount 0;

50 sents mechanical difdculti'es and according to an alternative suggestion, an alternating current is supplied to the amplifier after the first direct current amplification stage which serves as a carrier current for the photo-electric current varia- 56 tions. This alternating current which is moduit is desired to transmit, is arranged. The cylinder C carrying the picture is, for instance, given a rotational as well as lengthwise movement (not specifically illustrated in the drawing), whereby the picture is scanned along a spiral trace such 0 as is well known in the art. The picture is scanned by means of a light source L and an optical system 01, which concentrates the light emitted by the source L to'a small spot on the picture drum equal to the size of the elementary portions of the picture chosen for seaming purposes. The light reflected from theindividual picture elements under scanning, is collected by a further optical system 02 arranged at the side of reflected light which varies in accordance with the amount of brightness of the individual picture elements, is concentrated by an optical system 03, such as alens, and thrown upon the photo emitting electrode of the photo-electric cell P. This arrangement as described up to now, corresponds to the well-known apparatus used in practical picture telegraphy. The photoelectric cell is connected in series with an operating battery B1 to a coupling resistance R, which serves to transfer the current variations in the photo-electric circuit to the grid ofthe threeelectrode vacuum tube '1. The output circuit of the tube contains a repeater or transformer Tr. whose secondary may be connected to any wellknown type of amplifier, such as amplifiers commonly used in radio circuits.

In accordance with this invention, besides the light impinging on the photo-electric cell and originating from the picture scanning operation, the light emitted by a glow lamp G which is operated by an alternating current 0! a source S, is thrown on the photo emitting electrode, independent of the light rays originating from the picture scanning source L. Inthis manner, an alternating current modulated in accordance with the light intensities of the picture elements -is obtained in the output circuit of the photoelectric cell by the addition of the efiect o! the light rays originating from the picture scanning element and of thelightrays emitted by the glowing device G. This current may then easily theoretical graphs illustrating the physical phebe amplified by the well-known amplifiers which have been developed to a very high stage of dependability and efliciency. I

Referring to the Figures 2 and 3, which show nomenon involved, a represents the variations of the alternating voltage applied to the glow lamp device G. This voltage is preferably of sinusoidal shape'and may, for instance, be generated by a local vacuum tube oscillator. b constitutes the ignition voltage of the glow device and it is seen from Figure .2, that by properly choosing the amplitude of the supply voltage a in respect to the ignition voltage, the glow device is periodically lighted and extinguished in accordance with the alternating frequency 01' the supply voltage a.

In the diagram of Figure 2, the light periods are designated by 1 and the dark periods by d. This is due to the well-known fact that a glow lamp which usually consists of a vessel containing two electrodes and. being filled with a gas of appropriate nature and pressure, will light up whenever the value of the alternating current applied to the electrodes of the device exneeds the ignition voltage. The lamp will remain lighted as long as the alternating voltage is higher than the ignition voltage.

It is natural that in practical operationythe transition from light to dark periods and vice versa is not so sudden and abrupt as shown in Figure 2. The metal parts of the glow device after the decrease of the alternating voltage below the value of the ignition voltage, will exhibit an after-glow for a short period. This does not essentially change the shapeof the light curve as shown by Figure 2, but will merely have the effect of rounding oif its edges. The light values originating from'the' reflected light rays from the picture elements under scanning, are

T superimposed on the light impulses supplied by the glow lamp. This will produce a resultant current in the photo -electric cell such as shown by Figure 8. According to this figure, 1 represent, the light impulses produced by the glow lanip and 0 represents the light values supplied from the scanning apparatus superimposed upon the former- In this, w y. resultant impulses are vobtained whose. enveloping curve e varies in ac- ;cordance with the variations of the successively scanned elementary, picture portions. These impulses, which are. equivalent to a modulated carriercurrent', may then easily be translated by means of a succeeding vacuum tube '1', whereby preferably, the tube is given a negative bias to such an extent (f according to Figure 3), that only the upper parts containing the modulating variations of the resultant light impulses, are utilized and whereby, a purely modulated carrier current in the secondary of the transformer T: is obtained. H represents the usual heating battery for-the tube. T and B2 represents the anode supply source for the same. g, according to Figure 3, illustrates the operating characteristic of the tube T with its operating point at the most favorable position by providing a negative bias equal to f for cutting off the lower part of the resultant light impulses. In this manner, only the peak values which contain the low frequency modulation corresponding to the scanning values, are amplified in the output circuit of the tube as shown at h in Figure 3.

WhatI claim is:

, 1. In an electro-optical system, a photo-electric device,means for impinging a beam of light upon said device of varying intensity solely in accordance with modulating signals,'and further means for simultaneously impinging a separate beam of light of periodically fluctuating intensity upon said device for producing modulatedcarrier currents in the output circuit of said device.

2. In an electro-optical system, a photoelectric device, an object tobe scanned, a scanning beam of light of substantially constant intensity impinged'upon said object, means for impinging said beam upon said device after scanning said object, and means for producing a. further beam of light of periodically fluctuating intensity and simultaneously impinging said fluctuating beam upon said devicefor producing modulated carrier currents in the output circuit of said'device.

3. In combination in a photo-electric translating system, a photo-electric cell, an output circuit of said cell, a source of light of substantially constant intensity operating intermittently upon saidcell at a definite frequency, for producing photoelectric current impulses in saidoutput circuit, and a further source of light acting on said cell and varying in accordance with the quantity to bev translated for generating corresponding variations of photo-electric currents superimposed upon said first impulses, and a vacuum tube device having a cathode, anode and grid electrode with its grid circuit associated with said output circuit of said photo-electric cell and means to apply-a negative bias to said grid electrode for utilizing .only the upper portion of said superimposed resultant currents containing the current variations-corresponding to the variations of the quantityto be'translated by said system.

4. In combination in a photo-electric translating system, a photo-electric cell, an output circuit of said cell, an electric glow device influencing saidcell, an alternating voltage supply source for 'said glow device, the ignition voltage of said glow device being lower than the amplitude of said supply voltage, whereby said glow device is intermitfltently lighted and extinguished for producing responding variations of photo-electric current MI in said output circuit superimposed upon said current impulses.

5. In combination in a photo-electric translating system, a photo-electric cell, an output circuit of said cell, an electric glow device influencing 5 said cell, an alternating voltage supply source for said glow device, the ignition voltage of said glow device being lower than the amplitude of said supply voltage, whereby said glowdevice is intermittently lighted and extinguished for producing corresponding photo-electric current impulses in said output circuit, a further source of light operating on said cell and varying in accordance with the quantity to be translated to produce corresponding variations of photo-electric current in said output circuit super-imposed upon said current impulses, and a vacuum tube device havin its input circuit associated with said photoelectric cell.

6. In combination in a photo-electric translating system, a photo-electric cell, an output circuit of said cell, an electric glow device influencing said cell, an alternating voltage'supply source for said glow device, the ignition voltage or said glow device being lower than the amplitude of said supply voltage, whereby said glow device is intermittently lighted and extinguished for producing correspondingphoto-electric current impulses in said output circuit, a further source of light operating on said cell and varying in accordance with the quantity to be translated to produce corresponding variations of photo-electric current in said output circuit superimposed upon saidflrst current impulses, and a vacuum tube device having a cathode, anode and grid electrode, with its grid circuit being associated with said, output circuit and means to apply a negative bias to said grid ,electrode for utilizing only the upper portions of said resultant superimposed currents containing the variations of said quantity to be translated.

' 7. In combination in a picture transmission apparatus, a photo-electric cell, an electron emitting light sensitive electrode of said cell, a circuit or said cell, means to apply a beam of light to act upon said light sensitive electrode, varying in accordance with the brightness of successively scanned elementary portions 01 the picture to be transmitted to produce corresponding photo-electric current variations in said output circuit, and an electric glow device also acting on said light sensitive electrode, consisting of a gas-filled vessel with electrodes therein and a source or alternating voltage applied to said electrodes.

8. In combination in a picture transmission apparatus, a photo-electric cell, an electron emitting light sensitive electrode or said cell, a cirsuit of said cell, means to apply a beam of light to act upon said light sensitive electrode, varying in accordance with the brightness of successively scanned elementary portions oi the picture to be transmitted to produce corresponding photo-electric current variations in said output circuit, an electric glow device, also acting on said light sensitive electrode, consisting ota gas-filled vessel with electrodes therein and a source of alternating voltage applied to said electrodes, the igfiition voltage of said glow device being less than the amplitude of said alternating supply voltage for periodically lighting and extinguishing said glow device, for producing corresponding photo-electric current impulses insaid output circuit upon which said photo-electric current variations are superimposed.

9. In combination in a picture transmission apparatus, a photo-electric cell, an electron emitting light sensitive electrode or said cell, a circuit of said cell, means to apply a beam of light to act upon said light sensitive electrode, varying in accordance with the brightness or successively scanned elementary portions or the picture to be transmitted to produce corresponding photoelectric current variations in said output circuit, an electric glow device also acting ,onlsaid light sensitive electrode, consisting or,a gas-fll1ed vessel 105 with electrodes therein, a source of alternating 1 voltage applied to said electrodes, the ignition voltage of said glow device being less than theamplitude of said alternating supply voltage for periodically lighting and extinguishing said glow device, for producing corresponding photo-electric current impulses in said output circuit upon which said photo-electric current impulses in said output 'circiut upon which said photo-electric current variations are superim'pose and a vacuum tube 115 device having a cathode, an e and grid electrode with its grid associated with said output circuit, and means to apply a negative biasing voltage to said electrodegrid for utilizing only the upper portion of said resultant superimposed currents containing the variations corresponding to the brightness of elementary portions of the picture to be transmitted. 

